One of the problems affecting communication within a cellular telecommunications system is that of the interference generated by other communications of the cell or neighboring cells. A distinction is traditionally made between intercellular interference due to communication from neighboring cells and intra-cellular interference due to communications by the same cell where the terminal is located.
Many techniques have been proposed and implemented to reduce intra-cellular interference. Most of these techniques are based on an allocation of orthogonal transmission resources, for example time transmission intervals (TDMA), frequency transmission intervals (FDMA), OFDM orthogonal frequency-division multiplexing intervals (OFDMA), transmission codes (CDMA), transmission bundles (SDMA), or even a combination of such resources, so as to separate the different communications of a same cell.
Radio resources being rare, they are generally reused, at least in part, from one cell to the next. A radio resource management (RRM) module is then responsible for statically or dynamically allocating the radio resources to the different cells. It is in particular known to statically reuse radio frequencies following a bi-dimensional pattern (Frequency Reuse Pattern).
Due to the reuse of radio resources, a first communication between a first terminal and a first base station of a cell can be interfered with by a second communication, using the same radio resource, between a second terminal and a second base station of a neighboring cell. The situation is even more critical when the cells are adjacent and the terminals are on the cell border. In that case, the terminals must transmit at full power and the interference level is then higher.
For a given communication, here called first communication, the interference caused by a second communication using the same radio resource as the first is commonly called intra-band interference. In contrast, interband interference is the interference caused by a second communication using a distinct radio resource (for example a neighboring radio frequency or another radio interval) from that used by the first.
FIG. 1 shows a very simplified cellular telecommunications system, comprising two cells 151 and 152. The first cell 151 contains a first couple of terminals formed by a first transmitting terminal 110 and a first receiving terminal 120. Similarly, the second cell 152 comprises a second couple of terminals formed by a second transmitting terminal 130 and a second receiving terminal 140. Terminal here refers to a mobile terminal or a base station, or even a relay terminal in the case of a relayed channel. In particular, it will be understood that here we are considering both uplink and downlink communications. It is also assumed that the first communication between the terminals 110 and 120 uses the same radio resource(s) as the second transmission between the terminals 130 and 140 so that the two communications interfere with each other.
The processing and reduction of intercellular interference have been the subject of considerable research.
The simplest processing method is to consider the interference as a simple thermal noise. This processing method is only acceptable, however, if the interference level is low. It should be noted that most power allocation algorithms are based on this hypothesis.
Other processing methods make it possible to reduce the interference by estimating the information signal of the interfering communication(s). This assumes that the considered receiving terminal knows how to decode these information signals and consequently knows the codes having been used to encode them. Known amongst these methods are in particular PIC (Parallel Interference Canceller) or serial (Successive Interference Canceller) interference reduction plans, well known by those skilled in the art.
Another traditional approach for reducing the interference level is to implement an adaptive power control method. Such a method makes it possible to monitor the power levels of the different transmitting terminals so as to guarantee a predetermined service quality to the different users. This service quality can be measured depending on the case in terms of rate, latency, packet error rates, spatial coverage, etc. Traditionally, service quality metric refers to the parameter(s) used to measure it. As a general rule, a user's communication requires a minimum service quality that is taken into account or negotiated during the procedure to admit the user into the cell. This minimum service quality is expressed in the form of a stress on the service quality metric: latency below a threshold, rate greater than a guaranteed minimum, etc. The power allocation is then done so as to comply with the stress on the service quality metric.
Lastly, the power allocation can be handled in a centralized manner (Centralized Power Allocation) by a specific network node, NC (Network Controller), or in a distributed manner (Distributed Power Allocation) within each terminal.
Reciprocally, for a given transmission power stress, it is possible to seek to maximize the rates of different users, to increase the spatial coverage of different terminals, to reduce the latency for different communications, in other words to increase the service quality for different users. In this context, the service quality is expressed in the form of a so-called utility function relative to one or more users. For example, this utility function can be the sum of the rates of the different communications (Sum-Rate) or the minimum rate (Min-Rate) on those communications.
The known methods for processing the inter-cellular intra-band interference are relatively inflexible in that they do not adapt to the interference levels affecting the different communications.
A first problem at the base of the invention is consequently to propose a communication method for a wireless telecommunications system, in which the processing of the interference is adaptive as a function of the interference level.
Another problem at the base of the invention is to provide a power allocation method or a method for maximizing a utility function that takes this adaptive processing of the interference into account.